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- Author or Editor: Kenneth L. Steffen x
Chilling injury is more severe in the presence of light than in the dark. Anthocyanins, commonly found in the adaxial leaf layers of certain plants, are known to screen incident solar radiation. A correlation, between anthocyanin content and low temperature/light stress tolerance has been suggested. Our objective was to examine this relationship using purple-leaved (Pretty Purple) and green-leaved (Domino) pepper cultivars. At 5 weeks, Pretty Purple had a ca.10-fold higher anthocyanin content and a 50% higher chlorophyll content per area than Domino. Anthocyanins were observed in adaxial epidermal and palisade cells as well as in abaxial guard cells. Plants were grown at 25/20°C (day/night) before exposure to 4 days of chilling (8/5°C) followed by a 3 day recovery at 25/20°C. Light intensity was maintained at a constant level. Both cultivars demonstrated ca. 3-fold declines in light and bicarbonate-saturated photosynthesis following the chilling period with full recovery by 3 days. Quantum efficiency decreased ca. 3-fold in both cultivars with Domino exhibiting a more complete recovery. Variable Chl a fluorescence (Fv/Fm) decreased to 50% of control in Pretty Purple versus 25% of control in Domino, which conversely demonstrated a more complete recovery. The results suggest that anthocyanins may be protecting the photosynthetic apparatus and that differences may exist between cultivars in repair and/or energy quenching mechanisms.
Abstract
The effect of light stress following various levels of freezing stress on photosynthetic and respiratory functions in leaf tissue of Solanum acaule (Bitt.) was investigated under laboratory conditions. Terminal leaflets from plants grown at 18/16C (light/dark) and 400 μmol·s−1·m−2 photosynthetically active radiation (PAR) were slowly frozen in the dark to various minimum temperatures and then thawed on ice, also in the dark. Immediately after thawing, paired leaf disks were cut from a single terminal leaflet. Disks were then held at 1.0C for 3 hr, with one disk exposed to 800 μmol·s−1·m−2 PAR and the other disk of the pair was held in the dark. Our experimental approach allowed comparative studies on tissue from the same leaflet. Light during the post-thaw period, as compared to darkness, resulted in greater inhibition of photosynthetic processes, but had little effect on respiration. Our results demonstrate a) the importance of considering a light stress component during the assesment of relative frost tolerance in photosynthetic tissue and b) that chloroplast functions are much more sensitive than mitochondrial functions to a post-thaw light stress.
This study examined the effect of shifts in growth temperature on: 1) the partitioning of carbohydrate into starch or sucrose; and 2) the differential responses of tobacco types which differ in starch accumulation capacities. Six-week-old tobacco seedlings of Speight G28 (G28), a fluecured cultivar, and Ky 14 (K14), a burley cultivar, were acclimated for 9 days in growth chambers to a 14 h photoperiod of 300 μmol/s-m2 PAR at 27/22 C (day/night) and a relative humidity of between 70-80%. Temperature was then shifted to 15/10 C for 13 days and then back to 27/22 C for 8 days. At all points, sucrose, starch and protein content was higher in G28. Both cultivars demonstrated significant increases in dry matter accumulation per area, 1 day after the shift to 15/10 C. Dry matter increased steadily through day 13 in G28, but increased to day 5 and then leveled off at day 13 in K14. Nearly identical patterns of sucrose accumulation were observed in both species, with marked increases to day 5 and then a dramatic decline at day 13. Starch content increased steadily from day 1 to day 13 in G28, but leveled off in K14 after day 5. At day 8, soluble protein content increased only slightly in K14, but increased nearly 2-fold in G28. Within 1 day of the return to 27/22 C, starch and sucrose levels in both cultivars dropped 2 to 5-fold, to pre-temperature shift levels. The significance of these finding will be discussed.
Abstract
Three-week-old seedlings of the cabbage (Brassica oleracea L. Capitata group) cultivars Wisconsin All Seasons and Globe King were exposed for 3 weeks to Cu2+ concentrations ranging from 1.2 to 2.5 mg Cu2+/liter. Plants were harvested after 14, 16, 19, or 22 days of exposure. During Cu2+ treatment, shoots appeared healthy, but roots turned golden, with increased lateral branching and tip browning. Cultivars responded identically for all characteristics measured. Root Cu concentrations were >3000 μg·g−1 or 300 times the control after Cu2+ treatment. Shoot Cu concentrations (13 μg·g−1), while significantly higher than the control, were not above critical values associated with yield reductions. The high root Cu concentrations were not associated with lower shoot or root yields. The initial symptoms of Cu2+ toxicity in the first fully expanded leaves were elevated leaf Cu concentrations and lower total chlorophyll and chlorophyll a:b ratios. There was no effect on leaf fresh weight per unit area, transpiration, respiration, net photosynthesis, or apparent photosynthetic quantum yields.
We evaluated the effects of soil organic matter amendments on crop growth and yield over a three-year period. In Spring, 1990, we added 3.8 cm of spent mushroom compost and 1.3 cm of well-rotted horse manure to the top 0.2 m of selected plots in a 0.4 ha field. Other plots received recommended amounts of synthetic NPK. Total yield and yield of No. 1 grade tomatoes were 25% and 67% greater, respectively, in the amended plots than in the conventional plots the first year. In 1991, we no-till planted three varieties of sweet corn into this field. The conventional plots received either 75% or 100% of recommended N. Previously amended plots received no further N. Sweet corn production was 46-200% greater in amended plots, depending on variety. In 1992 following moldboard plowing, we planted snap beans followed by broccoli or cabbage. Conventional plots received the recommended amount of N (in 100% N plots from 1991) or no N (in 75% N plots from 1991) while plots amended in 1990 received no further N. Yields of snap beans were comparable in all three treatments. Broccoli heads had greater diameters in plots that had been amended. Cabbage from the amended plots were more mature based on growth stage. The beneficial effect of this initial amendment has continued for three growing seasons. This observation suggests that while the initial cost of organic soil amendments may be higher than synthetic fertilizer for the first year, comparable or greater yields may be expected allowing this approach to be cost-effective over a three-year period.
During the initial season of implementation, four tomato production systems differing in soil management, pest control practices, and level of inputs, such as labor, materials, and management intensity were evaluated. These systems were CON, a low input (no mulch, no trellising, overhead irrigation, preplant fertilization, scheduled pest control), conventional agrichemical system; BLD, a high input [straw mulch, trellising, trickle irrigation, compost fertility amendment, integrated pest management (IPM)], ecologically-oriented system that emphasized the building up of soil organic matter levels and used no agrichemicals to supply fertility or for pest control; BLD+, a system similar to BLD, except that agrichemical pesticides were used; and ICM, a high input system (black polyethylene mulch, trellising, trickle irrigation, fertigation, IPM pest control) that used agrichemicals to supply fertility and for pest control. Soil characteristics and fertility levels in the BLD and BLD+ systems were modified with extensive amendments of spent mushroom compost and well-rotted cattle manure. Levels of agrichemical NPK calculated to meet current crop needs were supplied to the CON and ICM systems, with 75% of fertility in the ICM system supplied through the trickle irrigation lines (fertigation). The BLD system had a greater soil water holding capacity and sharply reduced irrigation requirements. During a wet period, fruit cracking and evidence of water-mold root rot were significantly higher in the ICM system than the BLD and CON systems. Defoliation by Alternaria solani was greatest in the BLD system and least in the ICM system. The BLD and ICM systems resulted in a 1 week earlier peak yield compared to the CON system. The yield of No. 1 fruit was 55% to 60% greater in the BLD+ system than the other three systems, which were comparable in yield. Net return was highest in the BLD+ system, although the benefit/cost ratio was greatest in the CON system. This multidisciplinary study has identified important differences in the performance of diverse production systems during the unique transitional season.